CN114629089A - Single-ended-quantity waveform similarity protection method suitable for flexible direct-current transmission line - Google Patents

Single-ended-quantity waveform similarity protection method suitable for flexible direct-current transmission line Download PDF

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CN114629089A
CN114629089A CN202210246965.3A CN202210246965A CN114629089A CN 114629089 A CN114629089 A CN 114629089A CN 202210246965 A CN202210246965 A CN 202210246965A CN 114629089 A CN114629089 A CN 114629089A
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fault
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pole
voltage
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CN114629089B (en
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刘天琪
张雨晗
王顺亮
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Sichuan University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/088—Aspects of digital computing
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H1/00—Details of emergency protective circuit arrangements
    • H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/265—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured making use of travelling wave theory
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/28—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for meshed systems
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
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  • Locating Faults (AREA)
  • Emergency Protection Circuit Devices (AREA)

Abstract

The invention discloses a single-ended waveform similarity protection method suitable for a flexible direct-current transmission line, which is used for realizing reliable and quick protection of a fault pole line and reliable and immovable protection of a sound pole line by calculating an initial fault traveling wave and a reverse traveling wave based on phase-mode transformation, and calculating and judging internal and external faults of a region and determining a fault pole according to a wavelet transformation modulus maximum and waveform similarity. The invention only needs to utilize the single-ended voltage current traveling wave of the direct current line, has high reliability, and can accurately detect the fault line and the fault pole under different fault types, different fault resistances and different fault distances; the method has high selectivity, and can accurately judge the two-pole grounding fault which cannot be identified by the existing protection; the fault detection time meets the requirements. In addition, the protection method does not depend on high sampling rate, has strong anti-interference performance, is insensitive to the value of the current limiting reactor, the noise level and the start delay, and is suitable for different operation modes, thereby further improving the safety and the stability of the flexible direct current transmission system.

Description

Single-ended-quantity waveform similarity protection method suitable for flexible direct-current transmission line
Technical Field
The invention relates to a single-end-amount traveling wave waveform similarity protection method for a direct-current transmission line fault of a flexible direct-current transmission system, and belongs to the technical field of relay protection of power systems.
Background
The wide development and utilization of renewable clean energy sources such as water energy, wind energy, solar energy and the like are effective ways for dealing with fossil fuel crisis, environmental pollution and climate change. However, these resources are typically distributed in remote areas and these green powers can only be delivered to the load center by long-distance transmission techniques. Therefore, in order to receive and consume large-scale renewable clean energy and realize large-capacity long-distance transmission of green power, a flexible direct-current transmission technology is a feasible scheme. In addition, the method has the remarkable advantages of independent control of active power and reactive power, low line loss, asynchronous interconnection and the like. Meanwhile, the successful construction of the flexible direct current transmission project brings huge economic benefits and social benefits. Therefore, research based on the safety and stability of the flexible direct current transmission system can provide theoretical support for reliable and economic operation of the put-into-operation flexible direct current project.
Long-haul transmission typically employs overhead transmission lines, but more dc line faults occur than with cables. To reduce the destructive effects of a dc fault, the faulty dc line should be de-energized as soon as possible and isolated by a dc breaker, while the healthy dc line should continue to operate. However, the operation of the dc breaker must be controlled by the protection system. Therefore, the protection method of the flexible direct current transmission line is an important measure for ensuring the safe and stable operation of the flexible direct current transmission system. The direct current line protection system needs to accurately identify and only isolate a fault line and a fault pole, so that normal operation of a non-fault line and a healthy pole can be guaranteed; meanwhile, the method needs to have extremely high reliability, selectivity, speed and sensitivity.
Existing flexible dc transmission line protection schemes basically lend themselves to line protection in view of conventional hvdc transmission systems. The traveling wave protection and the differential under-voltage protection form main protection, and the pilot protection is used as backup protection. However, these protection schemes lack theoretical analysis for the development after line fault, and the protection principle only stays in the voltage and current break amount and micro level. In addition, the protection method is easy to reject or malfunction under the conditions of two-pole grounding fault, larger fault resistance, longer fault distance, noise signal interference and the like, and the reliability, selectivity, speed and sensitivity of the protection method are all to be improved.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a single-end-quantity waveform similarity protection method suitable for a flexible direct-current transmission line.
In order to achieve the purpose of the invention, the invention adopts the technical scheme that:
a single-ended waveform similarity protection method suitable for a flexible direct current transmission line comprises the following steps:
s1, the protection system collects and stores the voltage and the current of the positive and negative electrodes at the two ends of the flexible direct current transmission line in real time;
s2, detecting whether the direct current line where the protection system is located has a fault or not through a gradient voltage algorithm according to the voltage and the current of two poles of the direct current line, and starting protection if the protection criterion is met;
s3, after protection starting, performing fault component calculation and phase-mode conversion on the positive and negative voltage and current sampling values, and obtaining initial fault traveling waves and reverse traveling waves of the positive and negative voltage and current sampling values to obtain 0-mode initial fault voltage and current traveling waves, 1-mode initial fault voltage and current traveling waves, and 0-mode initial fault reverse traveling waves and 1-mode initial fault reverse traveling waves;
s4, calculating the modulus maximum value of the wavelet transform for the 1-mode initial fault voltage traveling wave of the direct current line, and intercepting T by the protection systemnTime window of length, based on the obtained TnJudging whether an in-region fault occurs or not according to the waveform similarity of the 1-mode initial fault voltage traveling wave and the reference voltage traveling wave of the length;
s5, calculating the modulus maximum value of wavelet transformation for the 0 mode and 1 mode initial fault reverse traveling wave of the direct current line, and intercepting Tn0And Tn1Time window of length, passing T n00 mode and T of lengthn1Determining a fault pole according to the ratio of the accumulated amplitude values of the 1-mode initial fault reverse traveling waves;
and S6, according to the judgment result, the protection system of the fault pole transmits an opening signal to the direct current breaker of the fault pole, so that the direct current breaker of the fault pole line can be ensured to be reliably and quickly moved, and the direct current breaker of the sound pole line can be ensured to be reliably and immovable.
Furthermore, the protection systems are respectively arranged at two ends of the flexible direct current transmission line and used for collecting and storing voltage and current in real time.
Further, the protection criterion in S2 is represented as:
Figure BDA0003545413760000031
wherein j ═ p/n represents a positive electrode/a negative electrode; u. ofj(t-i) is the voltage of the j-pole line at the ith sampling moment before the current sampling moment t;
Figure BDA0003545413760000032
the gradient voltage at the current sampling time t; Δ is the start cell threshold.
Further, the calculation of the fault component in S3 is disclosed as:
Figure BDA0003545413760000033
in the formula ujfAnd ijfThe voltage and current traveling waves are respectively generated after the j pole direct current line has a fault; u. ofjNAnd ijNThe voltage and current traveling waves of the j pole direct current line during normal operation are respectively; u. ofjAnd ijFault components of j-pole direct-current line voltage and current traveling waves are respectively;
the calculation formula of the phase-mode transformation in the S3 is as follows:
Figure BDA0003545413760000034
in the formula upAnd unInitial fault voltage travelling waves, i, of positive and negative dc lines, respectivelypAnd inInitial fault current traveling waves of the positive pole direct current line and the negative pole direct current line respectively; u. of0And u10-mode and 1-mode initiation of a DC line referenced to a positive voltage, respectivelyFault voltage travelling wave, i0And i1Respectively taking the positive pole current as the reference, and taking the 0 mode and the 1 mode of the initial fault current traveling wave of the direct current line;
the calculation formula of the reverse traveling wave in the S3 is as follows:
Figure BDA0003545413760000041
in the formula ur0And ur1Respectively are 0 mode and 1 mode initial fault reverse traveling waves of the direct current line; zc0And Zc1Representing the 0-mode and 1-mode wave impedances, respectively, of the dc line.
Further, in S4, a Mallat algorithm is used to calculate a wavelet transform modulus maximum of the 1-modulus initial fault voltage traveling wave of the dc line, and the time when the 1-modulus initial fault voltage traveling wave reaches the protection system is calibrated according to the wavelet transform modulus maximum, so as to determine the length of the time window;
the method for determining the length of the time window specifically comprises the following steps:
when the first wavelet transform modulus maximum value appears, the previous moment machine of the current moment is taken as TstartJudging whether a wavelet transform modulus maximum value appears in the next 1 millisecond of the current moment;
if the wavelet transform modulus maximum value does not appear in the next 1 millisecond, the time window is from TstartBeginning until 1 millisecond;
if the wavelet transform modulus maximum value appears again in the next 1 millisecond, the previous time of the time when the wavelet transform modulus maximum value appears again is recorded as TendIf the time window length is Tend-Tstart；
The basis for determining the intra-zone fault in S4 is:
Figure BDA0003545413760000042
in the formula uRRepresents a reference voltage traveling wave, u1Representing measured 1 at the head end of the protection system when a dc fault occursA traveling wave sampling value of the mode initial fault voltage; u. ofR(i) And u1(i) Each represents uRAnd u1The ith value of (d); n is the total number of sampling values, equal to the time window length TnMultiplying the sampling frequency; c (u)R,u1) Is the measured value of the partition unit of the protection system, and the value range is [ -1,1](ii) a -1 and 1 indicate that the two travelling waveforms are fully positively and negatively correlated, respectively; 0 means that the two traveling waves are completely different;
the method for judging the internal fault specifically comprises the following steps:
if c (u)R,u1) If the value is less than or equal to 0, no in-zone fault occurs;
if c (u)R,u1)>0, an intra-area fault occurs.
Further, the determination criterion of the fault pole in S5 is as follows:
Figure BDA0003545413760000051
in the formula, k is the measured value of the pole selection unit of the protection system; u. ur0And ur1Respectively representing the sampling values of 0-mode and 1-mode initial fault reverse traveling waves measured in the time window by the head end of the protection system when a fault occurs in the direct current area; u. ofr0(i) And ur1(i) Each represents ur0And ur1The ith value of (d); n is0And n1Each represents ur0And ur1The total number of sampled values of (a); n is0And n1Are respectively equal to the time window length Tn0And Tn1Multiplying the sampling frequency; the threshold values of the pole selection units are-1 and 1;
the fault pole determination method specifically comprises the following steps:
if k is larger than 1, determining that the anode fails;
if k is less than minus 1, determining that the negative pole is in fault;
and if k is more than or equal to negative 1 and less than or equal to 1, judging that the two electrodes have faults.
The beneficial effect of above-mentioned scheme is: the invention only needs to utilize the voltage and current traveling wave of the single end of the direct current line, does not need to communicate at two ends, has high reliability at the same time, and can accurately detect the fault line and the fault pole under different fault types (anode grounding, cathode grounding, interelectrode short circuit, two-pole grounding), different fault resistances (up to 500 omega) and different fault distances (full-line protection); the method has high selectivity, and can accurately judge the short-circuit fault of two-pole grounding (the anode grounding resistance is not equal to the cathode grounding resistance) which cannot be identified by the existing protection; high mobility, no communication delay, simple and reliable protection algorithm and fault detection time meeting requirements; and the sensitivity is high, and when the tail end of the direct current line has a fault (the fault resistance is 500 omega), the measured value of the partition unit is the largest and far exceeds the threshold value. In addition, the protection method does not depend on strict data synchronization and high sampling rate (not more than 100kHz), has strong anti-interference performance, is not sensitive to factors such as the value, the noise level and the start delay of the current limiting reactor, and is suitable for different operation modes. In summary, the protection method has good adaptability, has low requirements for popularization and application as main protection of the flexible direct current transmission line, can further improve the safety and stability of the flexible direct current transmission system, and ensures wide area complementation and flexible consumption of renewable clean energy.
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Fig. 1 is a schematic view of a specific process of the protection method of the present invention.
Fig. 2 is a schematic structural diagram of a flexible dc power transmission system in an embodiment of the present invention.
Fig. 3 is a schematic diagram illustrating a method for determining a time window when a dc fault occurs at an intra-area end according to an embodiment of the present invention.
Fig. 4 is a schematic diagram illustrating a method for determining a time window when a dc fault occurs in the middle of a zone according to an embodiment of the present invention.
FIG. 5 is a protection system PS for an out-of-range fault condition in an embodiment of the present invention14And (3) measured 1-mode initial fault voltage traveling waves and reference voltage traveling waves.
FIG. 6 shows a protection system PS under an intra-area fault condition according to an embodiment of the present invention14And (3) measured 1-mode initial fault voltage traveling waves and reference voltage traveling waves.
FIG. 7 shows a protection system PS for different fault resistances and different fault distances according to an embodiment of the present invention14Is calculated to obtainMeasured value of partition unit c (u)R,u141)。
FIG. 8(a), FIG. 8(b), FIG. 8(c), FIG. 8(d) are the protection system PS for four cases of the in-zone fault (fault distance of 0% and positive/negative fault resistance of 0 Ω/0 Ω, fault distance of 0% and positive/negative fault resistance of 0 Ω/500 Ω, fault distance of 100% and positive/negative fault resistance of 500 Ω/0 Ω) in the embodiment of the present invention, respectively14And (3) measuring the initial fault reverse traveling waves of the 0 mode and the 1 mode.
FIG. 9 shows a protection system PS for different fault resistances and different fault distances according to an embodiment of the present invention14And calculating the obtained measured value k of the pole selecting unit.
Fig. 10 is a schematic general flow diagram of a single-ended magnitude waveform similarity protection method applicable to a flexible direct-current transmission line according to the present invention.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.
A single-ended waveform similarity protection method applicable to a flexible dc transmission line, as shown in fig. 10, includes the following steps:
s1, the protection system collects and stores the voltage and the current of the positive and negative electrodes at the two ends of the flexible direct current transmission line in real time;
in this embodiment, as shown in fig. 2, which is a schematic diagram of a structure of a flexible dc power transmission system, for a line 14, a Protection System (PS) is provided14And PS41And a Direct current circuit breaker (Direct current breaker) DB14And DB41The two ends and two poles of the direct current circuit are matched with each other and are arranged. The protection area of the protection method is a direct current line with PS and DB, and limits at two ends of the direct current lineCurrent-limiting reactor L14And L41Defined and spaced apart by a distance of l14. The protection configuration of the remaining dc lines is similar to that of the dc line 14 and will not be described again.
Protection system PS with dc line 1414(including positive and negative electrode protection systems, and respectively mounted on the positive and negative electrodes of the circuit) as an example, f1Is an in-zone fault of the DC line, f2、f3、f4、f5、f6、f7、f8、f9、f10、f11、f12Are all out-of-range faults for the dc link. The main purpose of the protection method is to distinguish an intra-zone fault f1And an out-of-range fault, and detecting the fault pole (positive or negative or both) of the in-range fault line. The specific steps of this example are shown in fig. 1.
S2, detecting whether the direct current line where the protection system is located has a fault or not through a gradient voltage algorithm according to the voltage and the current of two poles of the direct current line, and starting protection if the protection criterion is met;
taking fig. 2 as an example of a flexible dc power transmission system, in this embodiment, the positive and negative protection systems PS14The voltage and the current of the positive pole and the negative pole of the flexible direct current circuit 14 are respectively collected and stored in real time, whether the direct current circuit 14 breaks down or not is detected through a gradient voltage algorithm, and the calculation formula is as follows:
Figure BDA0003545413760000081
wherein j ═ p/n represents a positive electrode/a negative electrode; u. of14j(t-i) is the voltage of the j pole of the direct current line 14 at the ith sampling moment before the current sampling moment t;
Figure BDA0003545413760000082
the gradient voltage of the j pole of the direct current line 14 at the current sampling time t; delta is the starting unit threshold, typically 0.1 kV.
If it is
Figure BDA0003545413760000083
If the absolute value of the gradient voltage is larger than the threshold value of the starting unit, the direct current line protection is started, and the fault line and the fault pole are further identified by using the started voltage and current sampling values of the positive pole and the negative pole.
S3, after protection starting, carrying out fault component calculation and phase-mode conversion on the positive and negative voltage and current sampling values, and obtaining initial fault traveling waves and reverse traveling waves of the positive and negative voltage and current sampling values to obtain 0-mode initial fault voltage and current traveling waves, 1-mode initial fault voltage and current traveling waves, and 0-mode and 1-mode initial fault reverse traveling waves;
taking fig. 2 as an example of a flexible dc power transmission system, after protection is started, the protection system PS14The fault component calculation and the phase-mode conversion are carried out on the positive and negative voltage current sampling values of the direct current line 14, and the initial fault traveling wave and the reverse traveling wave are obtained, so that the 0-mode initial fault voltage and the current traveling wave (u) of the direct current line 14 can be obtained140、i140) 1 mode initial fault voltage, current travelling wave (u)141、i141) And 0 mode, 1 mode initial fault reverse traveling wave (u)r140、ur141)。
The fault component calculation formula is as follows:
Figure BDA0003545413760000091
in the formula u14jfAnd i14jfVoltage and current traveling waves after the j pole of the direct current line 14 has a fault f; u. of14jNAnd i14jNVoltage and current traveling waves for normal operation of the j pole of the dc link 14, respectively; u. of14jAnd i14jThe j-pole voltage and current traveling wave fault components of the dc link 14, respectively.
The phase-mode conversion calculation formula is as follows:
Figure BDA0003545413760000092
in the formula u14pAnd u14nRespectively positive and negative dc linesInitial fault voltage travelling wave, i, of the way 1414pAnd i14nThe initial fault current traveling waves of the positive and negative dc lines 14, respectively; u. of140And u1410-mode and 1-mode initial fault voltage traveling waves i based on positive voltage140And i141The initial fault current traveling waves of the 0 mode and the 1 mode are respectively based on the anode current.
The formula of the reverse traveling wave calculation is as follows:
Figure BDA0003545413760000093
in the formula ur140And ur141Respectively 0 mode and 1 mode initial fault reverse traveling waves of the direct current line 14; zc0And Zc1Representing the 0-mode and 1-mode wave impedances, respectively, of the dc link 14.
In this embodiment, the Mallat algorithm is used to calculate the 1-mode initial fault voltage traveling wave (u) of the dc link 14141) And a Wavelet Transform Modulus Maximum (WTMM) of the wavelet and according to the WTMM pair u141Arrival protection system PS14Is calibrated to determine the time window TnLength of (d).
As shown in fig. 3 and 4, when the first WTMM (W) occurs whose absolute value is greater than the time window threshold (typically 20)startu141Equal to-181.6 and-719.4, respectively), this indicates that u141The head end protection system PS having reached the dc line 1414And the previous time of the time is recorded as Tstart. The length of the time window, however, varies depending on where the fault occurs, in particular in the following cases,
the first condition is as follows: as shown in fig. 3, the region f1Where a positive ground fault occurs (fault distance is 100% of the line 14, i.e. end, fault resistance is 500 Ω). If no WTMM satisfying the condition occurs within the subsequent 1 millisecond, the time window is from TstartBeginning until 1 ms later, in which case the time window length TnIs 1 millisecond;
case two: as shown in fig. 4, the region f1Where positive grounding occursFault (fault distance is 50% of line 14, i.e. middle, fault resistance is 0 Ω). The WTMM (W) satisfying the condition reappears in the subsequent 1 millisecondendu141Equal to-63.7), the time immediately preceding this time is taken as TendT in this casenIs Tend-Tstart。
S4, calculating the modulus maximum value of the wavelet transform for the 1-mode initial fault voltage traveling wave of the direct current line, and intercepting T by the protection systemnA time window of length based on the obtained TnJudging whether an in-region fault occurs or not according to the waveform similarity of the 1-mode initial fault voltage traveling wave and the reference voltage traveling wave of the length;
taking the figure 2 flexible dc transmission system as an example, 1 mode initial fault voltage traveling wave (u) through the dc link 14141) And reference voltage traveling wave (u)R) Judging whether the intra-area fault occurs according to the waveform similarity, wherein the calculation formula is as follows:
Figure BDA0003545413760000101
in the formula uR(i) And u141(i) Each represents uRAnd u141The ith value of (d); n is the total number of sampling values, equal to the time window length TnMultiplied by the sampling frequency, which in this embodiment is 100 kHz. c (u)R,u141) Is a protection system PS14The measured value of the partition unit of (1) can reflect uRAnd u141Waveform similarity of the traveling wave. If c (u)R,u141) If the value is 0 or a negative value, the condition that no in-zone fault occurs is indicated; if c (u)R,u141) If the value is positive, it indicates that an intra-area fault has occurred, and it is necessary to further determine the fault pole and the healthy pole.
The reference travelling wave u is shown in fig. 5RAnd u in case of different out-of-zone faults141The waveform of (2). "u" is a unit141[f6(PPG,0Ω)]"and" u141[f6(DPG,0Ω)]' direct current faults respectively representing positive electrode grounding (PPG) and two electrode grounding (DPG) and having fault resistance of 0 omega occur outside the protection area f6Time of flight protection system PS14U measured separately141. According to the protection criterion of the partition unit, the measured values of the partition unit are respectively c (u)R,u141[f6(PPG,0Ω)])＝-0.5688，c(uR,u141[f6(DPG,0Ω)]) -0.5763. As can be seen, c (u)R,u141) If the value is negative, it indicates that no intra-area fault occurs. In addition, the test results under various metallic out-of-area faults are given in table 1, and the test results do not meet the protection criteria. In table 1, "PPG, NPG, DPG, PP, O/TPG, SNT" respectively represent positive ground fault, negative ground fault, two-pole ground fault, inter-pole short-circuit fault, ac single-phase/three-phase ground fault, protection is not started, that is, the protection criterion of the starting unit is not satisfied.
TABLE 1 results of out-of-area fault testing
Figure BDA0003545413760000111
The reference travelling wave u is shown in fig. 6RAnd u under the condition of two-pole grounding fault in different areas141The waveform of (2). "u" is a unit141[f1(50％,0/500Ω)]"represents a DC fault f with two earthed poles and positive/negative fault resistances of 0/500 Ω1Protection system PS occurs at 50% (fault distance) of dc line 1414Measured u141. The rest of the legends have similar meanings and are not described in detail. As illustrated from left to right in fig. 6, c (u)R,u141) 0.4523, 0.8869 and 0.8887 are sequentially and respectively, and all the faults meet the criterion and are judged as the faults in the area.
In FIG. 7, f is shown1A positive earth fault occurs, and the system PS is protected under different fault distances (0% to 100%) and different fault resistances (0 Ω, 100 Ω, 500 Ω)14All the partition unit measured values are greater than 0, the protection criterion of the partition unit is met, and the partition unit is an intra-area fault. In addition, c (u)R,u141) The fault distance is reduced and the fault resistance is not sensitive, but the fault can be determined as an in-zone fault.
S5, for DC lineCalculating the maximum value of the wavelet transform modulus by the reverse traveling wave of the 0-mode and 1-mode initial fault, and intercepting Tn0And Tn1Time window of length, passing T n00 mode and T of lengthn1Determining a fault pole according to the ratio of the accumulated amplitude values of the 1-mode initial fault reverse traveling waves;
protection system PS14After the occurrence of the intra-area fault is judged, the reverse traveling wave (u) of the initial fault is obtained according to the 0 mode and the 1 mode obtained in the step (10)r140And ur141) The fault pole is determined by the ratio of the accumulated amplitude values, and the calculation formula is as follows:
Figure BDA0003545413760000121
in the formula ur140(i) And ur141(i) Each represents ur140And ur141The ith value of (d); n is0And n1Respectively representing the total number of sampling values of 0-mode and 1-mode initial fault reverse traveling waves of the direct current line 14, and intercepting Tn0U of lengthr140And Tn1U of lengthr141The method of time window can refer to the clipping method in step S3, and n0And n1Are respectively equal to the time window length Tn0And Tn1Multiplying the sampling frequency; k is the protection system PS14Measured value of the pole selection unit. If k is larger than 1, determining that the anode fails; if k is less than minus 1, determining that the negative pole is in fault; and if k is more than or equal to negative 1 and less than or equal to 1, determining that the two-pole fault comprises two-pole grounding fault and interelectrode short-circuit fault.
In fig. 8 u is shown for a two-pole earth fault situation in different zonesr140And ur141The waveform of (2). In fig. 8(a), the fault distance is 0% of the line 14, the positive fault resistance is 0 Ω, and the negative fault resistance is 0 Ω; in fig. 8(b), the failure distance is 0%, the positive failure resistance is 0 Ω, and the negative failure resistance is 500 Ω; in fig. 8(c), the failure distance is 100%, the positive failure resistance is 500 Ω, and the negative failure resistance is 500 Ω; in FIG. 8(d), in four cases where the failure distance is 100%, the positive failure resistance is 500. omega., and the negative failure resistance is 0. omega., k is-0.0015, 0.6670, -0.0025, -0.5148, and all are larger thanAnd if the voltage is equal to minus 1 and is equal to or less than 1, the two-pole fault is judged.
In FIG. 9, f is shown in the current zone1A positive earth fault occurs, the system PS is protected in the case of different fault distances (0% to 100%) and different fault resistances (0 Ω, 100 Ω, 500 Ω)14All the measured values of the selected pole units are more than 1, and the positive pole fault is judged. In addition, k is reduced as the fault distance becomes larger, and is insensitive to fault resistance, but can be determined as a positive fault.
And S6, according to the judgment result, the protection system of the fault pole transmits an opening signal to the direct current breaker of the fault pole, so that the direct current breaker of the fault pole line can be ensured to be reliably and quickly moved, and the direct current breaker of the sound pole line can be ensured to be reliably and immovable.
Taking the flexible direct current transmission system of fig. 2 as an example, according to the protection system PS14As a result of the determination, the fault pole protection system PS14Transmitting a trip signal to a fault pole dc breaker of the dc line 14, a sound pole protection system PS14And (6) locking.
In addition, tables 2 to 6 show the PS protection system under different internal and external faults and different sampling frequencies, values of the current limiting reactor, signal noise levels, start-up delay step lengths and operation modes, respectively14And measuring the calculated partition unit and pole selection unit measured values. Although c (u) varies with the value of interest in the above conditionsR,u141) And k also vary, but both faulty lines and faulty poles can be detected accurately.
Therefore, the protection method provided by the invention can accurately detect the fault line and the fault pole under different fault types, fault resistances and fault distances; in addition, the protection method does not depend on high sampling rate and strict data synchronization, has strong anti-interference performance, is insensitive to the value, noise level, start delay and the like of the current-limiting reactor, is suitable for different operation modes, can provide reliable action basis for subsequent fault clearing, further improves the safety and stability of the flexible direct-current transmission system, and ensures wide-area complementation and flexible consumption of renewable clean energy.
TABLE 2 sampling frequency test results
Figure BDA0003545413760000141
TABLE 3 Current limiting reactor test results
Figure BDA0003545413760000142
TABLE 4 Signal noise test results
Figure BDA0003545413760000143
TABLE 5 Start delay test results
Figure BDA0003545413760000151
Table 6 run mode test results
Figure BDA0003545413760000152
The principle and the implementation mode of the invention are explained by applying specific embodiments in the invention, and the description of the embodiments is only used for helping to understand the method and the core idea of the invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.
It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.

Claims (6)

1. A single-ended waveform similarity protection method suitable for a flexible direct current transmission line is characterized by comprising the following steps:
s1, the protection system collects and stores the voltage and the current of the positive and negative poles at the two ends of the flexible direct current transmission line in real time;
s2, detecting whether the direct current line where the protection system is located has a fault or not through a gradient voltage algorithm according to the voltage and the current of two poles of the direct current line, and starting protection if the protection criterion is met;
s3, after protection starting, carrying out fault component calculation and phase-mode conversion on the positive and negative voltage and current sampling values, and obtaining initial fault traveling waves and reverse traveling waves of the positive and negative voltage and current sampling values to obtain 0-mode initial fault voltage and current traveling waves, 1-mode initial fault voltage and current traveling waves, and 0-mode and 1-mode initial fault reverse traveling waves;
s4, calculating the modulus maximum value of the wavelet transform of the 1-mode initial fault voltage traveling wave of the direct current line, and intercepting T by the protection systemnTime window of length, based on the obtained TnJudging whether an in-region fault occurs or not according to the waveform similarity of the 1-mode initial fault voltage traveling wave and the reference voltage traveling wave of the length;
s5, calculating the wavelet transform modulus maximum value of the reverse traveling wave of the 0-mode and 1-mode initial faults of the direct current line, and intercepting Tn0And Tn1Time window of length, passing Tn00 mode and T of lengthn1Determining a fault pole according to the ratio of the amplitude accumulated values of the 1-mode initial fault reverse traveling waves of the length;
and S6, according to the judgment result, the protection system of the fault pole transmits an opening signal to the direct current breaker of the fault pole, so that the direct current breaker of the fault pole line can reliably and quickly move, and the direct current breaker of the sound pole line can reliably and fixedly move.
2. The single-ended-quantity waveform similarity protection method suitable for the flexible direct-current transmission line according to claim 1, wherein the protection systems are respectively arranged at two ends of the flexible direct-current transmission line and used for collecting and storing voltage and current in real time.
3. The single-ended waveform similarity protection method applicable to the flexible direct-current transmission line according to claim 1, wherein the protection criterion in S2 is represented as:
Figure FDA0003545413750000021
wherein j ═ p/n represents a positive electrode/a negative electrode; u. ofj(t-i) is the voltage of the j-pole line at the ith sampling moment before the current sampling moment t;
Figure FDA0003545413750000022
the gradient voltage at the current sampling time t; Δ is the start cell threshold.
4. The single-ended-quantity waveform similarity protection method applicable to the flexible direct-current transmission line according to claim 1, wherein the fault component calculation in the S3 is disclosed as:
Figure FDA0003545413750000023
in the formula ujfAnd ijfThe voltage and current traveling waves of the j-pole direct-current line after the fault occurs are respectively; u. ofjNAnd ijNThe voltage and current traveling waves of the j pole direct current line during normal operation are respectively; u. ofjAnd ijFault components of j-pole direct-current line voltage and current traveling wave are respectively;
the calculation formula of the phase-mode transformation in the S3 is as follows:
Figure FDA0003545413750000024
in the formula upAnd unAre respectively positiveInitial fault voltage traveling wave, i, of pole and cathode DC linespAnd inInitial fault current traveling waves of the positive pole direct current line and the negative pole direct current line are respectively; u. u0And u10-mode and 1-mode initial fault voltage traveling waves, i, of a direct current line based on a positive voltage0And i1Respectively taking the positive pole current as the reference, and taking the 0 mode and the 1 mode of the initial fault current traveling wave of the direct current line;
the calculation formula of the reverse traveling wave in the S3 is as follows:
Figure FDA0003545413750000025
in the formula ur0And ur1Respectively are 0 mode and 1 mode initial fault reverse traveling waves of the direct current line; zc0And Zc1Representing the 0-mode and 1-mode wave impedances, respectively, of the dc line.
5. The single-ended waveform similarity protection method applicable to the flexible direct-current transmission line according to claim 1, wherein in S4, a Mallat algorithm is adopted to calculate a wavelet transformation modulus maximum of a 1-mode initial fault voltage traveling wave of the direct-current line, and a time when the 1-mode initial fault voltage traveling wave reaches a protection system is calibrated according to the wavelet transformation modulus maximum to determine a time window length;
the method for determining the length of the time window specifically comprises the following steps:
when the first wavelet transform modulus maximum value appears, the previous moment machine of the current moment is taken as TstartJudging whether a wavelet transform modulus maximum value appears in the next 1 millisecond of the current moment;
if the wavelet transform modulus maximum value does not appear in the next 1 millisecond, the time window is from TstartBeginning until 1 millisecond;
if the wavelet transform modulus maximum value appears again in the next 1 millisecond, the previous time of the time when the wavelet transform modulus maximum value appears again is recorded as TendIf the time window length is Tend-Tstart；
The basis for determining the intra-zone fault in S4 is:
Figure FDA0003545413750000031
in the formula uRRepresents a reference voltage traveling wave, u1Representing a 1-mode initial fault voltage traveling wave sampling value measured by the head end of the protection system when a direct current fault occurs; u. ofR(i) And u1(i) Each represents uRAnd u1The ith value of (d); n is the total number of sampling values, equal to the time window length TnMultiplying the sampling frequency; c (u)R,u1) Is the measured value of the partition unit of the protection system, and the value range is [ -1,1](ii) a -1 and 1 indicate that the two travelling waveforms are fully positively and negatively correlated, respectively; 0 means that the two traveling waves are completely different;
the method for judging the internal fault specifically comprises the following steps:
if c (u)R,u1) If the value is less than or equal to 0, no intra-area fault occurs;
if c (u)R,u1)>0, an intra-zone failure occurs.
6. The single-ended-quantity waveform similarity protection method applicable to the flexible direct-current transmission line according to claim 1, wherein the judgment basis of the fault pole in the S5 is as follows:
Figure FDA0003545413750000041
in the formula, k is the measured value of the pole selection unit of the protection system; u. ofr0And ur1Respectively representing the sampling values of 0-mode and 1-mode initial fault reverse traveling waves measured in the time window by the head end of the protection system when a fault occurs in the direct current area; u. ofr0(i) And ur1(i) Each represents ur0And ur1The ith value of (d); n is0And n1Each represents ur0And ur1The total number of sampled values of (a); n is0And n1Are respectively equal to timeWindow length Tn0And Tn1Multiplying the sampling frequency; the threshold values of the pole selection units are-1 and 1;
the fault pole determination method specifically comprises the following steps:
if k is larger than 1, determining that the positive pole is in fault;
if k is less than minus 1, determining that the negative pole is in fault;
and if k is more than or equal to negative 1 and less than or equal to 1, judging that the two electrodes have faults.
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